The invention relates to a device for vacuum coating plain bearings. Plain bearings, also known as bearing shells, comprise concavely-curved surfaces, wherein the inner face associated with the shaft is provided with a multilayer system. Coating is effected in vacuum coating installations. Plain bearings of this type are mainly used under heavy loading in machine and vehicle construction.
Continuous installations for the vacuum coating of substrates have been known for a long time. The substrates may be of various materials and have varying dimensions and geometries, e.g. they may consist of strips, components or glass substrates. One or more layers are applied to these substrates in one pass. To this end, the substrates are introduced into the respective continuous installation via air-locks. Depending on the multilayer system to be applied, pre-treatment is conventionally carried out in an appropriate vacuum chamber, before the corresponding multilayer system is subsequently applied in one or more coating chambers. Once coating is complete, the substrate leaves the continuous installation via an air-lock. The entire multilayer system is applied in such continuous air-to-air installations. The substrates are moved at a virtually constant speed through the installation.
Where flat substrates, such as strips or glass sheets arranged in succession for example, are coated in a continuous installation of this type, it is also known to apply layers which differ in relation to material and thickness with different vacuum coating processes. Thus it is known to atomise two layers onto strips in one pass and then to apply a layer by vapour deposition (Surface and Coatings Technology, 93 (1997) pp. 51-57).
The continuous installation is suitable for strip-form material which is guided through the installation at the same speed even when undergoing different coating processes. However, this installation and the process carried out therewith have the disadvantage of not being suitable for coating substrates whose geometries and layer parameters and layer materials require varying conveying speeds and a variable conveying profile.
A continuous installation is also known for coating turbine blades (DE 195 37 092 C1). In this continuous installation, high temperature-resistant layers are applied to the turbine blades. Application of these layers is effected at high temperatures by electron beam vapour deposition, wherein the turbine blades have to be heated to temperatures of approximately 1000xc2x0 C. prior to coating. Coating at these temperatures requires highly complex apparatus, which is only warranted for special applications of this type, i.e. turbine blade coating. Coating is carried out by a single method only.
Methods and installations are additionally known for coating plain bearings. As batch installations these generally consist of a vacuum chamber, in which the final overlay is applied by sputtering, after pre-treatment, to a plain bearing which has already been coated. This overlay essentially determines the properties of the plain bearing. Whether the plain bearing fulfils the requirements of it depends on the quality of the overlay applied (DE 36 06 529 C2; AT 392 291 B).
A disadvantage is that, due to the nature of the process, application of the overlay by sputtering involves the input of a large amount of energy into the plain bearing. The temperatures at which the overlay, as a rule a tin-containing material, may be applied are restricted owing to the low melting point of the tin. For this reason, the application of high-quality overlays requires the energy introduced by the process to be reduced to a tolerable level by cooling, e.g. oil cooling. To this end, cooling fluid is supplied to and removed from each support in which the plain bearing is held during atomisation of the layer. Such cooling is unproblematic in batch installations. In contrast, coating of plain bearings in a coating installation of the continuous type, in which several layers are applied in succession under vacuum in vacuum chambers separated by air-locks, conventional fluid-cooling is possible only at great expense.
Another disadvantage of batch installations is that, as a result of magazine operation, they exhibit lower productivity than continuously or virtually continuously operated continuous installations. The lower productivity of batch installations is a consequence of their discontinuous operation and the frequent venting and ventilation of large parts of the installation.
A method for the production of plain bearings has been disclosed, in which the overlay is applied by electron beam vapour deposition. This method enables the overlay of plain bearings to be applied at a higher rate than when atomisation is used and at the same time allows a reduction in the energy input into the plain bearings (DE 195 14 836 A1). However, this method has not yet been applied industrially and at present there is no known installation in which this method may be carried out in relation to plain bearings under industrial conditions.
The object of the invention is to provide a device for vacuum coating plain bearings, with which it is possible to apply several layers of different materials in different thicknesses in highly efficient manner. The device is designed to permit high throughput at low cost. It is intended to ensure compliance with procedurally important parameters within narrow tolerance limits. The temperature of the plain bearing to be coated is to be kept constant within tight limits during the process. The installation is intended to be suitable for carrying out several vacuum processes necessary for the overall process.